engleski

Comparison of tufa from three locations in Croatia in terms of mineralogy, major and trace elements and specific activity

The process of tufa formation in Croatia has been studied the most intensively in Plitvice Lakes and Krka River by Srdoč et al. (1985), Horvatinčić et al. (1989) and many others. In the recent paper by Horvatinčić et al. (2000), ages were reported by U-Th and 14C dating methods. It was concluded that the growth of tufa is restricted to the warm periods of global climate and was interrupted during glacial, stadial and interstadial periods. In the present paper selected samples of tufa from three different locations (Plitvice Lakes, Krka River and Mrežnica River) in Dinaric Karst of Croatia were characterized in terms of mineralogical composition, major and trace elements and specific activity. All tufa deposits contained calcite as the major mineral. From minor minerals dolomite was found in tufa from Krka River and quartz in tufa from Mrežnica River. The content of calcium carbonate varied form 71.5 to 97.5%, of magnesium carbonate from 0 to 6.6%. From other available elements the most abundant is iron, from 0.016 to 2.7%. Many other trace elements are also present. Specific activity of radionuclides 40K, 232Th, 137Cs, 226Ra and 238U showed different concentrations in all samples. In most samples, particularly in Plitvice Lakes, the ratio 238U/236Ra deviates from theoretical value 1, suggesting different transport of this elements into tufa. Specific activity of 137Cs does neither correlate with mineralogical composition, nor with the age determined by Horvatinčić et al. (2000). Relatively high 137Cs concentration in some samples can be explained by pollution after accident in Tchernobyl in 1986.

tufa formation; mineralogy; trace elements; specific activity; dating

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